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Over the years, I have received many questions about financial calculators. I will compile a list of the most frequently asked questions here.

Q: My 10B (or 10BII) is showing a comma instead of a decimal point. How do I fix this problem?

A: This is easily the most commonly asked question. I wish I knew how people got themselves into this situation, because it seems unlikely that it could happen by accident. Here is how to solve the problem: Press Shift . (decimal point).

A little background on this. In the U.S. and many other countries, we use a decimal point as the radix point (or decimal separator) and a comma as the thousands separator. Many other countries do exactly the opposite. For a complete list, see the decimal separator article on Wikipedia. Interestingly, as far as I can tell this has nothing to do with the side of the road on which you drive. Obviously, the 10B (and 10BII) was created with worldwide users in mind.

Q: How do I change the number of decimal places that are displayed?

A: Simply press Shift = and then a number key. For example, to display five decimal places, press Shift = 5.

Q: What batteries does the HP 10B or HP 10BII use?

The HP 10B (the older version) uses three 357 batteries. The HP 10BII (newer version) uses two 2032 batteries. In both cases the batteries are very easy to change by simply opening the battery cover on the back side of the calculator.

Q: How do I enter a negative number into one of the TVM keys on the HP 10B (or 10BII)?

A: The way to do it is by using the +/- (change sign) key. For example, to enter -1,000 into FV, press 1000 +/- FV.

Q: How do I find roots other than square roots using the HP 10B (or 10BII)?

In finance it seems that we are forever calculating various roots (cube root, fourth root, 365th root, etc). Fortunately, this is pretty simple to do if you can remember a simple mathematical rule:

nth root formula

So, to calculate the 5th root of 100, we simply raise 100 to the 1/5th power. To do this on the 10B type: 100 yx 5 1/x =. In this example, the 5th root of 100 equals 2.51189. Note that after you press yx the screen will say "Pending" because the calculator is waiting for you to complete the data entry. Using this technique you can calculate any root.

Q: My calculator only has a key to calculate natural logarithms. How do I calculate logarithms to other bases (say, base 10)?

A: Most often, in finance, we use natural logarithms (base e), usually abbreviated as Ln(x). However, sometimes we need to use other bases. Converting from base e to any other base can be done with the following formula (I'm converting to base 10):

logarithm base conversion formula

So, just calculate the natural log of your number, and then divide it by the natural log of the new base. For example, Log10(3) = Ln(3)/Ln(10) = 0.478.

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